C++ 如何检查 STL 迭代器是否指向任何东西？
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How to check whether STL iterator points at anything?
提问by James Hopkin
Possible Duplicate:
C++ Best way to check if an iterator is valid
可能的重复：
C++ 检查迭代器是否有效的最佳方法
I want to do something like this:
我想做这样的事情：
std::vector<int>::iterator it;
// /cut/ search for something in vector and point iterator at it.
if(!it) //check whether found
do_something();
But there is no operator! for iterators. How can I check whether iterator points at anything?
但是没有运营商！对于迭代器。如何检查迭代器是否指向任何内容？
回答by James Hopkin
You can't. The usual idiom is to use the container's end iterator as a 'not found' marker. This is what std::findreturns.
你不能。通常的习惯用法是使用容器的结束迭代器作为“未找到”标记。这就是std::find返回。
std::vector<int>::iterator i = std::find(v.begin(), v.end(), 13);
if (i != v.end())
{
// ...
}
The only thing you can do with an unassigned iterator is assign a value to it.
对于未分配的迭代器，您唯一可以做的就是为其分配一个值。
回答by aJ.
Though the iterators are considered as general form of pointers, they are not exactly the pointers. The standard defines Past-the-enditerator to indicate the search failure in containers. Hence, it is not recommended to check the iterators for NULL
尽管迭代器被认为是指针的一般形式，但它们并不完全是指针。该标准定义了Past-the-end迭代器来指示容器中的搜索失败。因此，不建议检查迭代器是否为 NULL
Past-the-endvalues are nonsingular and nondereferenceable.
Past-the-end值是非奇异的和不可解引用的。
if(it != aVector.end()) //past-the-end iterator
do_something();
回答by Xeningem
If you want to use iterator in a loop, the safest way to use it is in this fashion:
如果你想在循环中使用迭代器，最安全的使用方式是这样的：
for (std::vector<int>::iterator it = v.begin(); it != v.end(); ++it)
{
do_smth();
}
回答by Xeningem
I believe this should generally give you a good test:
我相信这通常应该给你一个很好的测试：
if (iterator._Mycont == &MyContainer)
{
Probably a valid iterator!
}
You could do tests to make sure that the iterator does not equal the end...
您可以进行测试以确保迭代器不等于结束...
iterator != MyContainer.end()
and:
和：
iterator >= MyContainer.begin()
